Extended abstract for the 21st International Geophysical Conference and Exhibition, Sydney, 2010

Knowledge of the degree of damage to residential structures expected from severe wind is used to study the benefits from adaptation strategies developed in response to expected changes in wind severity due to climate change, inform the insurance industry and provide emergency services with estimates of expected damage. A series of heuristic wind vulnerability curves for Australian residential structures has been developed for the National Wind Exposure project. In order to provide rigor to the heuristic curves and to enable quantitative assessment to be made of adaptation strategies, work has commenced by Geoscience Australia in collaboration with James Cook University and JDH Consulting to produce a simulation tool to quantitatively assess damage to buildings from severe wind. The simulation tool accounts for variability in wind profile, shielding, structural strength, pressure coefficients, building orientation, component self weights, debris damage and water ingress via a Monte Carlo approach. The software takes a component-based approach to modelling building vulnerability. It is based on the premise that overall building damage is strongly related to the failure of key components (i.e. connections). If these failures can be ascertained, and associated damage from debris and water penetration reliably estimated, scenarios of complete building damage can be assessed. This approach has been developed with varying degrees of rigor by researchers around the world and is best practice for the insurance industry. This project involves the integration of existing Australian work and the development of additional key components required to complete the process.

Atmospheric CO2 perturbations from simulated leaks have been used to determine the minimum statistically significant emissions that can be detected above background concentrations using a single atmospheric station. The study uses high precision CO2 measurements from the Arcturus atmospheric monitoring station in the Bowen Basin, Australia. A statistical model of the observed CO2 signal was constructed, combining both a regression and a time series model. A non-parametric goodness of fit approach using the Kolmogorov-Smirnoff (KS) test was then used to test whether simulated perturbations can be detected against the modelled expected value of the background for certain hours of the day and for particular seasons. The KS test calculates the probability that the modelled leak perturbation could be caused by natural variation in the background. Using pre-whitened data and selecting optimum test conditions, minimum detectable leaks located 1 km from the measurement station were estimated at 22 tpd for an area source of size 100 m x 100 m and 14 tpd for a point source at a KS cutoff defined by using the formal p-value of 0.05. These are very large leaks located only 1 km from the station and have a high false alarm rate of 56%. An alternative p-value could be chosen to reduce the false alarm rate but then the minimum detectable leaks are larger. A long term, single measurement station monitoring program that is unconstrained by prior information on the possible direction or magnitude of a leak, and based solely on detection of perturbations of CO2 due to leakage above a (naturally noisy) background signal, is likely to take one or more years to detect leaks of the order of 10 kt p.a. The sensitivity of detection of a leak above a background signal could be greatly improved through the installation of additional atmospheric monitoring stations or through greater prior knowledge about the location and size of a suspected leak.

This paper discusses two of the key inputs used to produce the draft National Earthquake Hazard Map for Australia: 1) the earthquake catalogue and 2) the ground-motion prediction equations (GMPEs). The composite catalogue used draws upon information from three key catalogues for Australian and regional earthquakes; a catalogue of Australian earthquakes provided by Gary Gibson, Geoscience Australia's QUAKES, and the International Seismological Centre. A complex logic is then applied to select preferred location and magnitude of earthquakes depending on spatial and temporal criteria. Because disparate local magnitude equations were used through time, we performed first order magnitude corrections to standardise magnitude estimates to be consistent with the attenuation of contemporary local magnitude ML formulae. Whilst most earthquake magnitudes do not change significantly, our methodology can result in reductions of up to one local magnitude unit in certain cases. Subsequent ML-MW (moment magnitude) corrections were applied. The catalogue was declustered using a magnitude dependent spatio-temporal filter. Previously identified blasts were removed and a time-of-day filter was developed to further deblast the catalogue.

Terrain affects optical satellite images through both irradiance and BRDF effects. It results in the slopes facing toward the sun receiving enhanced solar irradiance and appearing brighter compared to those facing away from the sun. For anisotropic surfaces, the radiance received at the satellite sensor from a sloping surface is also affected by surface BRDF which varies with combinations of surface landcover types, sun, and satellite as well as topographic geometry. Consequently, to obtain comparable surface reflectance from satellite images covering mountainous areas, it is necessary to process the images to reduce or remove the topographic effect so that the images can be used for different purposes. The most common method of normalising for the topographic effect is by using a Digital Surface Model (DSM). However, the accuracy of the correction depends on the accuracy, scale and spatial resolution of DSM data as well as the co-registration between the DSM and satellite images. A physically based BRDF and atmospheric correction model in conjunction with the 1-second SRTM derived DSM product were used to conduct the analysis. The results show that artefacts in the DSM data can cause significant local errors in the correction. For some areas, false shadow and over corrected surface reflectance factors have been observed. In other areas, the algorithm is unable to detect shadow or retrieve an accurate surface reflectance factor. The accuracy of co-registration between satellite images and DSM data is important for the topographic correction. A mis-registration error of one or two pixels can lead to large error in the gully and ridge areas. Therefore, accurate registration for both satellite images and DSM data is necessary to ensure the accuracy of the correction. Using low resolution DSM data to correct high resolution satellite images can fail to correct some significant terrain effects.

Strong evidence for at least one active Palaeozoic petroleum system in the undrilled northern Arafura Basin is provided by a new geological framework study, based on seismic and new well interpretations, and a seepage survey. Evidence for hydrocarbon generation is provided by oil and gas shows and indications and interstitial solid bitumens in wells in the Goulburn Graben, SAR anomalies, and shallow gas indications in sub-bottom profile, side-scan sonar and echosounder data. Deposition in the Arafura Basin commenced in the Neoproterozoic during a period of upper crustal extension that resulted in the formation of large NE-SW trending half graben. The overlying Palaeozoic section is more or less structurally conformable, despite long periods of non-deposition and erosion. Potential source rocks were deposited in the Middle Cambrian, Late Devonian and Late Carboniferous to Early Permian, in shallow-marine and deltaic environments. In comparison with the highly-deformed Goulburn Graben in the southern part of the basin, the northern Arafura Basin has undergone only minor deformation. As a result, many of the risk factors for the accumulation of hydrocarbons identified in the Goulburn Graben, such as timing of generation and expulsion, and reservoir quality, are reduced in this region. New geohistory models suggest that early expelled hydrocarbons are likely to be preserved in the northern Arafura Basin, and that in some locations, expulsion from Early Palaeozoic source rocks occurred in the Mesozoic to Cenozoic. Early formed traps are likely to have remained intact and reservoir quality should be higher as a result of reduced hydrothermal alteration and/or shallower burial.

Approximately 75% of Australia is covered by public-domain, airborne gamma-ray spectrometric surveys. However, all the older surveys are in units of c/s and their data values depend on the survey instrumentation and acquisition parameters. Also, many of the newer surveys were inadequately calibrated with the result that data values on adjacent surveys are not necessarily comparable. This limits the usefulness of these data Geoscience Australia and State Geological Surveys are working towards establishing a national baseline database of Australian gamma-ray spectrometric data that is consistent with the global radioelement baseline. This will be achieved by: (a) ensuring consistency in the calibration and processing of new gamma-ray spectrometric data through the use of standard processing procedures and calibration facilities that are tied to the global datum, and; (b) adjusting older surveys to the global datum through back-calibration and automatic grid merging. Surveys that are registered to the same datum are easily merged into regional compilations which facilitate the recognition and interpretation of broad-scale regional features, and allow lessons learnt in one area to be more easily applied to other areas.

Introduction Low-density geochemical surveys provide a cost-effective means to assess the composition of near-surface materials over large areas. Many countries in the world have already compiled geochemical atlases based on such data. These have been used for a number of applications, including: - establish baselines from which future changes can be measured - design geologically sensible targets for remediation of contaminated sites - support decision-making regarding appropriate land-use - explore for natural resources - study links between geology and plant/animal health (geohealth) A first pilot project was initiated to help establish sampling and analytical protocols relevant to Australian landscapes and climates. The Riverina region was chosen for this study because of its crucial economic, environmental and societal importance within the Murray-Darling basin. The region is a prime agricultural area, is bordered to the south by the Victorian goldfields, and is home to 11% of the Australian population. Results of this study are presented here. Methods Using a hydrological analysis, 142 sites near the outlets of large catchments were selected within the 123,000 km2 survey area (1 site per 866 km2 on average). At each site, two 10-cm thick overbank sediment samples were taken, one at the surface ('top overbank sediment', TOS) and the other between 60 and 90 cm depth (`bottom overbank sediment', BOS). These were described, dried, sieved (<180 m) and analysed chemically for 62 elements. Exploratory data analysis was undertaken and geochemical maps (various styles are shown here) were prepared. Results and discussion The geology of the area is dominated by Cainozoic sediments found in low-relief plains over the vast majority of the Riverina. The eastern and southern fringes of the area form higher relief landforms developed on outcropping or subcropping Palaeozoic sedimentary, mafic and felsic volcanic and felsic intrusive rocks. The geochemical results of the survey are independently corroborated by the good match between the distributions of K, U and Th concentrations in TOS and airborne gamma-ray maps. The distribution of Ca in BOS indicates generally higher concentrations in the northern part of the study area, which is also reflected in higher soil pH values there. Such data have implications for soil fertility and management in agricultural areas. In terms of applications to mineral exploration, dispersion trains of typical pathfinder elements for gold mineralisation, like As and Sb are clearly documented by the smoothly decreasing concentrations from south (near the Victorian goldfields) to north (over sediments from the Murray basin). Chromium is an element that can be associated with ill-health in animals and humans when present over certain levels. There is a smooth increase in Cr concentration from north to south, and the two sites with the highest values can be correlated with a ridge of Cambrian mafic volcanics. High total Cr concentrations in the Riverina are unlikely, however, to lead to serious health problems as only a very small proportion of Cr will be bioavailable. Conversely, some elements can be present at concentrations that are too low for optimum plant growth, such as potentially Mo. The distribution map for this element shows a general decrease from south to north. Given its lower bioavailability in acid soils, Mo is likely to be deficient in the south of the region, despite higher total concentrations here. Farmers report the necessity to use Mo-enriched fertilisers in this area. Conclusions Low-density geochemical surveys can be conducted in Australia using common regolith sampling media. They provide a cost-effective, internally consistent dataset that can be used by to support a variety of critical economic, environmental and societal decisions.

Australia's marine jurisdiction is one of the largest and most diverse in the world and surprisingly our knowledge of the biological diversity, marine ecosystems and the physical environment is limited. Acquiring and assembling high resolution seabed bathymetric data is a mandatory step in achieving the goal of increasing our knowledge of the marine environment because models of seabed morphology derived from these data provide useful insights into the physical processes acting on the seabed and the location of different types of habitats. Another important application of detailed bathymetric data is the modelling of hazards such tsunami and storms as they interact with the shelf and coast. Hydrodynamic equations used in tsunami modelling are insensitive to small changes in the earthquake source model, however, small changes in the bathymetry of the shelf and nearshore can have a dramatic effect on model outputs. Therefore, accurate detailed bathymetry data are essential. Geoscience Australia has created high resolution bathymetry grids (at 250, 100, 50 and 10 metres) for Christmas, Cocos (Keeling), Lord Howe and Norfolk Islands. An exhaustive search was conducted finding all available bathymetry such as multibeam swath, laser airborne depth sounder, conventional echo sounder, satellite derived bathymetry and naval charts. Much of this data has been sourced from Geoscience Australia's holdings as well as the CSIRO, the Australian Hydrographic Service and foreign institutions.Onshore data was sourced from Geoscience Australia and other Commonwealth institutions. The final product is a seamless combined Digital Bathymetric Model (DBM) and Digital Elevation Model (DEM).The new Geoscience Australia grids are a vast improvement on the existing publicly available grids.

Geoscience Australia (GA) has developed an interactive 3D virtual globe viewer to present global, national and regional scale geoscience data to government, geoscience industries, the scientific community and the general public. The interactive virtual globe is built on NASA's open source World Wind Java Software Development Kit (SDK) and provides users with easy and rich access to a growing number of geoscience datasets, including subsurface data, from within GA and around the world. The tool has been used by GA as a platform for the public launch of a number of national datasets, including the Radiometric Map of Australia, the Magnetic Anomaly Map of Australia and the Gravity Anomaly Map of Australia. More recently it has been used to display sub-surface datasets such as seismic and airborne electromagnetic data (AEM) alongside other relevant geoscience data to facilitate effective communication of scientific findings. In this paper the authors address the considerations used for selecting the World Wind SDK over other solutions, the current state of the 3D viewer tool, including display of subsurface data, and the benefits that GA has seen from its adoption.